The present invention relates to the operation of a gas turbine, and more particularly to a method for operating an air preheating system integrated with a gas turbine.
Turbomachines, such as gas turbines, aero-derivatives, or the like, commonly operate in a combined-cycle and/or cogeneration mode. In combined-cycle operation, a heat recovery steam generator, which generates steam, receives the exhaust-gas from the gas turbine; the steam then flows to a steam turbine that generates additional electricity. In a co-generation operation, a portion of the steam generated by the heat recovery steam generator is sent to a separate process requiring the steam.
Combined-cycle and cogeneration plants are rated to generate the maximum amount of energy (mechanical, electrical, etc) while operating at baseload. However, baseload operation, though desired by operators, is not always feasible. There may not be a demand in the energy market (electrical grid, or the like) for all of the energy generated at baseload. Here, the powerplant must either shutdown or operate at partload, where less than the maximum amount of energy is generated. Furthermore, partload operation tends to decrease the overall efficiency and increase the heatrate of the powerplant.
Gas turbines are typically required to maintain emissions compliance while generating power. A gas turbine operating at partload, may not maintain emissions compliance over the entire partload range, (from spinning reserve to near baseload). Turndown range may be considered the loading range where the gas turbine maintains emissions compliance. A broad turndown range allows operators to maintain emissions compliance, minimize fuel consumption, and avoid the thermal transients associated with shutting down the powerplant.
An air preheating system may reduce the extent of the aforementioned disadvantages associated with operating a gas turbine at partload. For the foregoing reasons, there is a need for a method of operating a gas turbine integrated with an air preheating system. The method should allow for extending the turndown range. The method should allow for a reduction in the fuel consumed by the gas turbine while operating at the partload range.